Light harvesting complex protein

Characterization of the Light-Harvesting Complex Proteins of the Photosystems in Control and Chi b-less Mutant... 

The results described above show a truncated Chi antenna size for PSI and PSII in the Chi b-less mutant. Consequently, the amount of light harvesting complex proteins should be accordingly reduced in the mutant relative to the control. The amount and composition of the LHC proteins was determined in western blots by using polyclonal antibodies that cross-react with the LHC proteins of both PSII and PSI [Bassi and Wollman 1991, Bassi et al. 1992]. Figure 5 shows the cross-reaction of at least 8 protein bands with these polyclonal antibodies. These bands originated either from LHC-II or LHC-I polypeptides. 

The antennae complexes (light harvesting complex proteins or LHCs) are a large family of related proteins that bind xanthophylls (typically lutein, violaxanthin and neoxanthin), Chi a and Chi b and collectively are the most abundant pigment protein complexes in the plastid (Peter and Thomber, 1991 Bassi et al., 1993). 

Despite considerable efforts very few membrane proteins have yielded crystals that diffract x-rays to high resolution. In fact, only about a dozen such proteins are currently known, among which are porins (which are outer membrane proteins from bacteria), the enzymes cytochrome c oxidase and prostaglandin synthase, and the light-harvesting complexes and photosynthetic reaction centers involved in photosynthesis. In contrast, many other membrane proteins have yielded small crystals that diffract poorly, or not at all, using conventional x-ray sources. However, using the most advanced synchrotron sources (see Chapter 18) it is now possible to determine x-ray structures from protein crystals as small as 20 pm wide which will permit more membrane protein structures to be elucidated. 

Given the difficulty of obtaining three-dimensional crystals of membrane proteins, it is not surprising that the electron microscope technique is now widely used to study large membrane-bound complexes such as the acetylcholine receptor, rhodopsin, ion pumps, gap junctions, water channels and light-harvesting complexes, which crystallize in two dimensions. 

TTie reaction center is surrounded by a ring of 16 antenna proteins of the light-harvesting complex LHl... 

Pullerits T. and Sundstrom V. (1996) Photosynthetic Light-Harvesting Pigment-Protein Complexes Toward Understanding How and Why, Acc. Chem. Res. 29, 381-389. 

A. Imaging Aggregates oe the Green Plant Light-Harvesting Pigment-Protein Complex LHCM... 

FIGURE 4.5 Aggregates of light-harvesting pigment-protein complex (LHCll) imaged with (a) MPF, (h) SHG, and (c) THG contrasts. The scale har is 3 pm. 

Biological systems Ligand-myoglobin Protein dynamics Bacteriorhodopsin Light harvesting Pigment-protein complexes Photosynthetic reaction centers... 

Eukaryotic plants and cyanobacteria. Photosynthetic dinoflagellates, which make up much of the marine plankton, use both carotenoids and chlorophyll in light-harvesting complexes. The carotenoid peridinin (Fig. 23-29), which absorbs blue-green in the 470- to 550-nm range, predominates. The LH complex of Amphidinium carterae consists of a 30.2-kDA protein that forms a cavity into which eight molecules of peridinin but only two of chlorophyll a (Chi a) and two molecules of a galactolipid are bound (Fig. 23-29).268... 

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